The present invention relates to reflective insulation and, in particular, it concerns flexible reflective insulating structures for various uses.
Different types of insulation products reduce the heat transferred by conduction, convection and radiation to varying degrees. As a result, each provides different thermal performance and corresponding xe2x80x9cRxe2x80x9d and xe2x80x9cUxe2x80x9d values (used to quantify heat transfer properties). The primary function of reflective insulation is to reduce radiant heat transfer across open spaces, which is a significant contributor to heat gain in summer and heat loss in winter. The low emittance metal foil (usually aluminum) surface of the product blocks up to 97% of the radiation and therefore a significant part of the heat transfer.
Aluminum foil is not, by itself, an effective thermal insulator. On the contrary, it is a metal with a relatively high thermal conductivity. When, on the other hand, a foiled surface is adjoined by a xe2x80x9cstillxe2x80x9d airspace, a reflective space acts as an insulating barrier as it retards radiant read (irrespective of heat flow direction) and thus reduces thermal transfer. In this context, it should be noted that the term xe2x80x9creflectivexe2x80x9d, as used in reflective insulation, is in some ways a misnomer because the aluminum either works by reflecting heat (reflectance of 0.97) or by not radiating heat (emittance of 0.03). Whether stated as reflectivity or emittance, the performance (heat transfer) is the same.
The magnitude of that reduction of heat transfer is dependent upon maintaining the integrity of the airspace from a structural standpoint. The overall thermal efficiency of an airspace will vary with the content of moisture (which increases the thermal conductivity of air) and the presence of convective currents. The performance of reflective surfaces in radiant barrier insulators is enhanced by providing, maintaining and insuring an optimum adjoining airspace.
Currently available reflective insulating products have reflective surfaces on one or both outward-facing surfaces of a core medium. Such products, however, suffer from numerous shortcomings. Specifically, such products are only effective when used in conjunction with a structure for ensuring an airspace adjacent to the reflective surfaces. This generally adds very significant labor costs to installation of the insulation. Furthermore, the properties of the reflective surfaces are extremely prone to degradation due to deposition of dust and dirt, and effects of corrosion on the surfaces. Thus, an aluminum surface of initial emittance 0.03 may frequently be found to exhibit emittance values ten or more times greater due to accumulation of dirt. In moist or otherwise aggressive environments, the degradation may be greatly accelerated by corrosion of the metal surfaces. In cases of applications in the building industry, such as within cavity walls, dust present during installation may reduce the effectiveness of the insulation from the outset such that the theoretical values are never actually obtained.
In an attempt to address these problems of degradation, U.S. Pat. No. 4,247,599 to Hopper proposes a layered structure which includes an intermediate metal layer is covered by a protective layer of polyethylene which is relatively transparent to infrared. The primary low-emittance characteristic is provided by an exposed outer metal layer while the intermediate metal layer provides a xe2x80x9cfail-safe featurexe2x80x9d should the exposed metal layer be completely degraded.
The solution proposed by Hopper offers very inferior results due to the lack of an airspace adjacent to the intermediate metal layer. Thus, despite the relative transparency of the polyethylene. Hopper admits that the metal-polyethylene combination exhibits an actual emittance value of 0.35, more than ten times greater than that of aluminum exposed directly to an airspace.
An alternative approach to guarding the integrity of the reflective surfaces is to provide reflective surfaces facing inwards towards airspaces defined by an internal structure. Examples of systems of this type are described by U.S. Pat. Nos. 3,616,139 to Jones and 5,230,941 to Hollander et al. These patents disclose reflective insulation panels made up of a honeycombed paper structure enclosed by inward facing foil reflective surfaces to form an insulative reflective space.
While the panels of Jones and Hollander et al. may provide highly effective insulation, their usefulness is limited by the rigid nature of the panels. Specifically, the panels are bulky and awkward to transport, and cannot be used at all in a wide range of applications for which flexible insulating materials are required.
Finally, U.S. Pat. No. 5,549,956 to Handwerker discloses a reduced thickness flexible insulating blanket for use in the curing of concrete. The blanket includes one or more heat reflective layer of aluminum foil adjacent to an insulative layer of xc2xc or xc2xd inch thickness bubble-pack type material. The bubbles are disposed in spaced relation so as to define between them open air spaces adjacent to the foil.
The blanket of Handwerker also suffers from various shortcomings. Firstly, the contact surface of the insulative layer with the reflective layer is relatively high. Although not described in detail, it appears from the illustrations that contact occurs over approximately 25% of the reflective surface, thereby greatly reducing the effectiveness of the reflective insulation. Additionally, the use of thin insulative layers containing open spaces with unrestricted air movement provides low resistance to conductive and convective heat transfer through the blanket. Finally, any attempt to produce thicker, more effective insulation by using multiple layers would reduce the flexibility of the blanket and lead to a bulky structure which would be costly and inconvenient to transport and handle.
There is therefore a need for flexible reflective insulating structures which would provide non-exposed reflective layers adjacent to an effective airspace which would also offer effective insulation against conductive and convective heat transport. It would also be highly advantageous to provide flexible reflective insulating structures which could be compactly stored and transported while being deployable to occupy an increased volume.
The present invention provides flexible reflective insulating structures for use in buildings, tents and other applications.
According to the teachings of the present invention there is provided, a flexible reflective insulating structure comprising: (a) a layer of substantially non-dust-generating, flexible fiber-based material; and (b) a flexible metallic layer having a first surface of emissivity less than 0.1, and preferably no more than 0.05, the metallic layer being attached to the layer of fiber-based material with the first surface facing towards the layer of fiber-based material in a manner such that the emissivity of at least about 85% of the first surface, and preferably at least about 95%, and most preferably at least about 97%, is substantially unaffected.
According to a further feature of the present invention, the layer of fiber-based material is a non-woven material.
According to a further feature of the present invention, the non-woven material is configured to be compressible to a compressed state for rolling to a rolled storage configuration and to recover when unrolled to an uncompressed state, the non-woven material occupying a volume when in the uncompressed state which is at least about two times a volume occupied by the non-woven material when in the compressed state.
According to a further feature of the present invention, the non-woven material has a bulk density of no more than about 4 kg/m2, and preferably within the range from about 0.9 to about 2 kg/m2, per 10 cm thickness when in the uncompressed state.
According to a further feature of the present invention, the layer of fiber-based material is formed primarily from polyester fibers.
According to a further feature of the present invention, the layer of fiber-based material includes crimped fibers.
According to a further feature of the present invention, the layer of fiber-based material exhibits a reduced density of fibers in a layer adjacent to the metallic layer relative to an average density of fibers in the fiber-based material.
According to a further feature of the present invention, the layer of fiber-based material includes a first component of fibers having a first diameter and a second component of fibers having a second diameter, the second diameter being at least twice the first diameter.
According to a further feature of the present invention, the layer of fiber-based material is a woven material, the woven material being processed to provide a plurality of raised fibers projecting outwards from the woven material for supporting the metallic layer.
According to a further feature of the present invention, the metallic layer is a sheet of metal foil.
According to a further feature of the present invention, the sheet of metal foil has a second surface opposite to the first surface, the insulating structure further comprising a substrate layer attached to the second surface.
According to a further feature of the present invention, the substrate layer is formed primarily from polymer material.
According to a further feature of the present invention, the polymer material has a thickness of at least 50 xcexcm and contains at least one additive chosen to enhance weatherproof properties of the polymer material.
According to a further feature of the present invention, the polymer material is selected to be a non-tearing material, the polymer material, the metallic layer and the fiber-based material being sewed together.
According to a further feature of the present invention, there is also provided a sealant applied to the structure so as to seal regions which are sewed together.
According to a further feature of the present invention, the layer of polymer material includes a plurality of reinforcing element.
According to a further feature of the present invention, there is also provided a second metallic layer associated with a rear surface of the substrate layer.
According to a further feature of the present invention, the metallic layer is implemented as a layer of metal deposited onto a surface of a flexible substrate layer.
There is also provided according to a further feature of the present invention, a tent comprising at least one wall formed from the insulating structure of the present invention.